This invention relates to an apparatus to cook food with steam. The benefits of cooking with steam as opposed to alternative methods are appreciated by many concerned with the nutritive value as well as the aesthetic qualities of food.
Raw foodstuffs such as meats and vegetables are made up of cells which have a high water content. When such foods are cooked under dry conditions, as when baked, they lose intrinsic moisture and may become less palatable and less attractive. When food is cooked by immersion in boiling water, the water in the food cells will expand and also boil, breaking down cell membranes and walls. The result is not only a deterioration in texture but also a loss of flavor and color as soluble cell contents are diluted away.
Even at room temperature, the quality of food is affected when it is immersed in water. Osmotic effects will cause cells to expand and rupture in hypotonic environments and to shrink in those that are hypertonic. Equilibrium forces cause a redistribution of ions and small molecules between intercellular and extracellular compartments which can be detrimental to flavor and nutritive value. These effects proceed more rapidly as the temperature is increased.
An ideal device then should cook food in a moist atmosphere, below the boiling point of water, and without allowing it to become saturated with water.
Existing cooking devices, such as the double boiler, the pressure cooker and variants of vessels containing racks to suspend food over boiling water do not achieve all of these objectives.
A double boiler consists of a pot for holding food which is nested into another containing boiling water. The food is out of contact with water and the temperature in the upper pot cannot exceed the steam temperature, however, since the steam does not penetrate the food but only contacts the exterior of the cooking pot, the method is only suitable for heating liquids, which can conduct and distribute the heat. Food cooked on a rack in a pressure cooker is penetrated by steam and suspended above the water level; however, the purpose of this method is to reduce cooking times, a purpose achieved by increasing the pressure so that the temperature can be raised above the atmospheric boiling point of water. Such temperatures, even in the absence of boiling, can adversely affect food textures. The simple process of cooking food over boiling water on a rack in a covered vessel comes close to the ideal method, but in practice, steam condenses on the inside of the vessel lid and drips back into the food. Since condensate is cooler than the steam, it interrupts the cooking process in local regions where it falls and the cooked food lacks uniform texture. Further, soluble constituents of the food are leached away as condensate percolates down through. The double boiler and pressure cooker devices suffer these drawbacks as well.
The present invention makes it possible to cook food uniformly and at a constant temperature below the boiling point of water by means of steam, at ambient pressure. It avoids the contact of condensate with food by providing a means to divert it from the compartment in which food is cooked and return it to a reservoir.